In the 1+1 line protection, under the Optical Terminal Multiplexer (OTM)-OTM single-span or multi-span scenario, the transmitting end of the Optical Line Protector (OLP) uses the 50:50 coupler to perform an equal light splitting of the signal light and then transmits the split signal lights to the main and standby optical lines, while the receiving end of the OLP selects and receives the split signal light using an optical switch. Under the application scenario of OTM-OTM single-span or multi-span transmission, since the transmitting end uses the 50:50 coupler, the optical transmission line system introduces an extra loss about 3 dB. When the transmission distance of the optical transmission line system exceeds a certain value, the 3 dB loss will have a large influence on the performance of the optical transmission line system (the optical power budget at the receiving end and the signal-to-noise ratio), and thus, the configuration scheme of the optical transmission line system needs to be changed.
In order to solve the problem of 3 dB insertion loss introduced by the transmitting end of the OLP using the 50:50 coupler in the 1+1 line protection, the existing 1:1 line protection can be adopted. In the conventional art, the 50:50 coupler may be replaced with an Optical Switch (OSW) at the transmitting end of the OLP, and selectively transmit the signal light to the main or standby optical line, and the receiving end selects and receives the signal light using the OSW.
However, a synchronous handover is required between upstream and downstream of the 1:1 line protection, thus the complicated handshake protocol shall be employed between the upstream and downstream of the 1:1 line protection. The upstream and downstream ensure the completion of the protection handover through multiple times of handshakes, thus the switching reliability is decreased, and the switching time is longer than that of the 1+1 line protection.